1. Field of the Invention
The invention relates to hydraulic damping rubber mounts and, more particularly, to hydraulically damped rubber engine mounts for motor vehicles.
2. Description of the Prior Art
Rubber mounts are used as mounts for drive systems in all types of motor vehicles. In mounts for internal combustion engines in motor vehicles, it is necessary on one hand to prevent noise vibration transmission, which has been achieved in the prior art by the use of a mount which is as soft as possible, and which has low self-damping. Unfortunately, a soft mount allows the movements of the motor excited by the roadway to become large which may cause bottoming of the mounts. On the other hand, the large movements of the engine in its mounts can be reduced by the use of hard engine mounts or separate vibration damping, but that leads to significant noise transmission to the body of the motor vehicle.
Rubber mounts of the prior art are known, for example, from European Patent Publication Published For Opposition Purposes No. 27 751, which has good damping in the range of low frequencies. A disadvantage here, however, is the fact that above a determined vibration amplitude or a determined frequency, cavitation occurs in the chamber, which leads to undesirable noise. Such cavitation occurs whenever, during the occurrence of large vibrations, the damping fluid flows from one chamber into the other chamber, and a vacuum forms in front of a region or point for relieving the pressure difference, since the fluid equilibrium cannot be established rapidly enough.
In the previous German Patent Application No. P 32 46 205.0, the problem of cavitation has already been addressed and solved. But this apparatus has a partition, which has a rigid middle region, and an elastic outer region which opens a bypass under conditions of pressure or vacuum build-up. As a result of the rigid central portion of the partition and the pressure relief point located in this portion, large masses must be moved when the bypass is opened, since the pressure relief point itself must also be moved. In addition, appropriate and expensive metal parts are necessary for clamping the partition.